Optogenetics, as known in the art of neuroscience and electro-physiology, is the combination of genetic and optical methods to control specific events in targeted cells of living tissue, particularly within living organisms such as mammals and other animals, with the temporal and spatial precision needed to keep pace with functioning intact biological systems. Millisecond-scale temporal precision and micrometer-scale spatial resolution are central to optogenetics. This allows experimenters to keep pace with fast biological information processing, for example, by probing the causal role of specific action potential patterns in defined neurons.
In electro-physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell or neuron rapidly rises and falls within a voltage range of about 100 micro-volts. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine cells, as well as some plant cells. Action potentials may be recorded with small metal electrodes placed next to a cell or neuron, but a main problem of this approach is that of obtaining electrodes small enough to record voltages within a single axon without perturbing it, and that of overcoming the electrical capacitance effects of the cell or neuron.
Optical imaging technologies have been developed in recent years to measure action potentials using voltage-sensitive dyes. Such optogenetic technologies involve the combination of optical, electrical and fluidic functionalities all at once for the study and control of action potentials in living organisms. The hallmark of optogenetics is the introduction of fast light-activated channels that allow for the temporally precise manipulation of electrical and biochemical events while maintaining cell-type spatial resolution.
Optogenetics typically operates at the millisecond timescale to allow for the monitoring, the addition or the deletion of precise activity patterns within specific cells in the brains of intact animals, including mammals. By comparison, the temporal precision of traditional genetic manipulations conventionally employed to probe the causal role of specific genes within cells, via “loss-of-function” or “gain of function” changes in these genes is rather slow, from hours to days.
Optogenetics typically also operates at the micrometer scale to allow for spatial resolution of precise activity patterns, for example within specific cells in the brains of intact animals, including mammals. By comparison, the spatial resolution of bundles traditionally used in optogenetics, including electrodes, tubules and fiber-optic bundles, is of the order of 1 millimeter at best, which is inappropriate to resolve features as small as a cell or a neuron.
Today's optogenetics technology generally borrows the technology used in endoscopy which employs large, millimeter-scale assemblies of fiber-optic bundles, metallic wires and fluidic tubules, or a partial combination thereof, that do not meet the spatial resolution nor the minimalist invasion required for probing living tissues.
U.S. Pat. No. 5,419,312 issued to I. K. Arenberg provides a multi-functional endoscope apparatus which includes a specialized system for illuminating the interior of a body cavity and directing the resulting images outwardly from the cavity for observation. It also includes a sub-system for delivering laser light to the body cavity for treatment purposes in a safe and effective manner for both the patient and treating physician, and it incorporates a sub-system for sensing temperature and fluid pressure levels within a body cavity, and a sub-system for sensing electrical potentials generated within tissues. This document addresses the need for an endoscope system suitable for use in narrow body cavities, such as the inner ear, but does not meet the requirement of micrometer-scale resolution for sensing individual cells or neurons as required in optogenetics.
Medical procedures employing probes inserted into a patient's organs borrow the technology of laser probes for eye surgery as illustrated in U.S. Pat. No. 5,643,250 (the '250 patent), issued to F. E. O'Donnell, Jr., and in U.S. Pat. No. 6,520,955 (the '955 patent), issued to M. Reynard.
The '250 patent discloses a laser probe which includes a fiber-optic channel and an infusion port for irrigating solutions to be infused into an eye during laser surgery on cornea tissue. However, the laser probe diameter may not allow insertion through numerous layers and densities of tissues disposed between a dermal surface and internal organs disposed medially within a patient.
The '955 patent discloses a process and apparatus for removing cataract tissue in an eye and for injecting a lens replacement material into the eye lens to fill the intralenticular space. The apparatus disclosed in the '955 patent includes a needle having dual cannula oriented as coaxial annular conduits through which chemicals and enzymes are delivered into cataract tissue. A separate focused laser is used to destroy the cataract tissue, followed by decomposed cataract tissue being removed by aspiration through an aspiration instrument or through a coaxial annular conduit of the needle.
However, the '250 and the '955 patents do not provide means for impressing electrical voltage or electrical current to the tissue which is a desirable feature in optogenetics.
U.S. Pat. No. 7,292,758 issued to M. Bayindir provides a fiber photodetector comprising: a semiconducting element having a fiber length and being characterized as a non-composite semiconducting chalcogenide glass material selected from the group consisting of (As40Se60)1-xSnx, As40Se50Te10Sn5, and As2Se3, in at least one fiber direction; at least one pair of conducting electrodes in contact with the semiconducting element along the fiber length; and an insulator along the fiber length. Although this fiber can be scaled down to address some optogenetics applications, fluidic functionalities are not provided. In addition, the fiber photodetector disclosed in this patent raises serious concerns regarding the toxicity of the arsenic-based glass compositions therein.
A recent publication by Y. LeChasseur et al. in Nature Methods, vol. 8 no. 4, p. 319 (2011) describes the development of an optogenetic unit for electro-physiology comprising a dual optical core and an electrolyte-filled electrical core. This design enables the fabrication of optogenetic probes as small as 10 μm, combining electrical and optical detection with single-cell optical resolution at a depth of >6,000 μm in the intact central nervous system. However, the probes exhibit very high electrical resistance (6-26 MOhm), which may limit certain types of recordings due to insufficient signal-to-noise ratio. Moreover, there are no provisions for fluidic delivery functionalities.
Also known in the art are the following patents and patent applications:
U.S. Pat. No. 7,773,647U.S. Pat. No. 7,846,391U.S. Pat. No. 7,837,654U.S. Pat. No. 6,568,219U.S. Pat. No. 6,432,851U.S. Pat. No. 6,995,101U.S. Pat. Pub. No. 2011/0094584A1
In light of the above, it can be seen that existing optogenetic devices and methods lack the full set of attributes desired for providing a functional and minimally-invasive optogenetic probe. There is therefore a need in the fields of neuroscience and electro-physiology for an optogenetic probe that overcome or at least alleviates at least some of these drawbacks.